Ignore changes to target group arns in nomad-cluster ASG

modules/nomad-cluster/main.tf

@@ -49,6 +49,18 @@ resource "aws_autoscaling_group" "autoscaling_group" {
       propagate_at_launch = tag.value["propagate_at_launch"]
     }
   }
+
+  lifecycle {
+    # As of AWS Provider 3.x, inline load_balancers and target_group_arns
+    # in an aws_autoscaling_group take precedence over attachment resources.
+    # Since the consul-cluster module does not define any Load Balancers,
+    # it's safe to assume that we will always want to favor an attachment
+    # over these inline properties.
+    #
+    # For further discussion and links to relevant documentation, see
+    # https://github.com/hashicorp/terraform-aws-vault/issues/210
+    ignore_changes = [load_balancers, target_group_arns]
+  }
 }
 
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